This invention relates to an apparatus for measurement of a spectrum of alpha emissions from a radioactive source.
Radiochemical analysis of materials is important to the determination of elements that emit alpha particles, such as plutonium, at environmental levels. For monitoring purposes, it is useful to be able to detect with accuracy the concentrations of both man-made alpha-emitting nuclides and those that occur naturally. Such determinations are commonly made by separating the alpha emitter chemically from the other constituents of a sample and measuring the amount of the alpha emitter by placing it close to a surface-barrier detector, evacuating the region between them, and connecting the surface-barrier detector as a diode in an external circuit that measures current pulses through the detector under suitable conditions of bias. Each such current pulse represents a disintegration producing an alpha particle and the count of such disintegrations over a known period of time provides a measure of the amount of the alpha emitter. Spectral information is also available from the detected pulses. Several manufacturers produce commercial chambers designed to support a surface-barrier detector in a fixed position near a planchet containing radioactive material. Such chambers also provide means for establishing a vacuum sufficient to avoid interference with the count.
All of the test chambers that are commercially available suffer from one or more of the following disadvantages. Some lack protection for the surface-barrier detector. They expose the detecting surface to the possibility of being touched by the alpha emitter, by a support tray or by the finger of an operator. Any such contact with the detector may damage or destroy it. Some suffer from a lack of facility for reproducibly placing the alpha emitter in close proximity to the detector. Some chambers that are commercially available cause delays in beginning measurement by the time taken to pump down a test chamber that has a volume that is large in comparison with the volume of the actual measuring region.
It is an object of the present invention to make a better chamber for measuring alpha radiation from alpha emitters.
It is a further object of the present invention to provide a test chamber for alpha spectrometry that protects a detector from accidental contact.
It is a further object of the present invention to provide a test chamber for alpha spectrometry that has a minimum pumpout volume.
It is a further object of the present invention to increase the reproducibility of positioning of an alpha emitter near a detector.
Other objects will become apparent in the course of a detailed description of the invention.